A magnetic recording disk comprises mainly a cartridge case (i.e., cartridge or jacket) having a magnetic head-inserting gate and a hole for rotation-driving, a flexible magnetic recording disk rotatably loaded in the cartridge case and a liner provided on the inside of the above cartridge case.
A liner of a conventional magnetic recording disk comprises a nonwoven fabric made of a mixed yarn of a rayon fiber and a polypropylene fiber, a polyethylene terephthalate fiber, a mixed yarn of an acrylic fiber and a polyester fiber, or a mixed yarn of an acrylic fiber and a rayon fiber. The liner is fixed on the inside of the cartridge case, for example, by heat fusion and an adhesive.
In general, the flexible magnetic disk has on one side or both sides of a nonmagnetic support of polyester film or the like, a magnetic layer formed by coating on the support a magnetic coating solution prepared by dispersing and mixing a binder, a dispersant, a lubricant and an abrasive in an organic solvent, or by directly depositing a ferromagnetic metal by vacuum deposition. Further, the discoid magnetic recording medium comprises mainly a cartridge case having a magnetic head-inserting gate and a hole for rotation-driving and has a liner for supporting the magnetic recording medium.
Binders for a magnetic recording medium include synthetic resins such as a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, a polyurethane resin, a polyester resin, a cellulose derivative, a synthetic rubber type resin, an epoxy resin, an isocyanate type resin, and an acrylic type resin.
Further, the above magnetic layer may contain various additives such as a dispersant, a lubricant and an antistatic agent. These additives are usually various organic compounds such as, for example, fatty acids and their derivatives (fatty acid esters, fatty acid metal salts and fatty acid amides), aliphatic ethers, aliphatic alcohols, and aliphatic ketones as well as compounds having a saturated or unsaturated hydrocarbon group.
The materials for the liner are natural and synthetic fibers such as cellulose, rayon, polypropylene, polyethylene terephthalate, polyacrylic ester, and nylon. Mixed and impregnated into these fibers are each of a dispersant, a smoothing agent and an antistatic agent in an amount of each component of from 0.1 to 0.5% by weight. The above mixed solution is known as an oil solutions such as polyoxyethylene, glycol fatty acid ester and sodium alkylsulfuric acid ester. A nonwoven fabric is formed from the fibers singly or in combination, and the nonwoven fabric thus prepared is used in a single layer or a multilayer.
However, the compounds present in the binder and various additives contained in the magnetic layer are the nutritive sources for molds.
These substances help molds to grow on the surface of the medium in the high humidity. These molds are deposited on the surface of the disk and are liable to create problems such as a dropout.
It is proposed in JP-A-61-241212 and JP-A-2-49217 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application") to add an antimold agent to a magnetic layer to prevent mold from growing on the magnetic recording disk. JP-A-62-252582, JP-A-62-281176, JP-A-61-258075 and JP-A-63-157876 propose improving the material of a liner. However, these techniques are insufficient to prevent molds in the high humidity. Further, there are no countermeasures, for example, for a running durability in the high humidity where ferromagnetic powder, as discussed below, is used for a high density recording.
To increase the recording density of the recording medium, the recording capacity must be increased from 1M to 4M and further to 10M. In order to attain an increase in recording capacity, ferromagnetic metal powders consisting mainly of Fe, Ni and Co and tabular hexagonal ferrite powders such as barium ferrite have been investigated as ferromagnetic powders used for the recording medium.
Ferromagnetic metal powders are suitable for a high density recording medium because of their excellent magnetic properties such as coercive force and saturation magnetization. The tabular hexagonal ferrite powders are advantageous because of the easiness in utilizing a vertical magnetization component of the magnetic layer due to an axis of easy magnetization existing in the direction vertical to the plate of the grains thereof. In combination with the above properties, the recording density can be further increased by using the ferromagnetic metal powders having a specific surface area of 30 m.sup.2 /g or more and a crystallite size of 300 .ANG. or less measured by an X-ray diffraction method and the tabular hexagonal ferrite powders having a specific surface area of 25 m.sup.2 or more, a tabular ratio (tabular diameter/tabular thickness) of 2 to 6 and a grain length as small as 0.02 to 1.0 .mu.m.
Usually, a liner comprising a nonwoven fabric, which is provided on the inside wall of a jacket (i.e., cartridge) for the purpose of cleaning and protecting the surface of a magnetic layer, protects the magnetic layer without scratching the surface thereof or increasing torque at whatever condition the magnetic recording disk is used. However, where ferromagnetic metal powders and tabular hexagonal ferrite powders each having a small grain size are used as described above in order to increase recording density of a magnetic recording disk, the magnetic layer sometimes is rubbed and scratched by the liner present between a jacket (i.e., a cartridge or a jacket) and the flexible magnetic disk. Further, where these powders are used in high humidity, torque sometimes is increased which prevents the disk from smoothly rotating.
The above problems cannot be sufficiently solved merely by incorporating abrasive particles and fatty acid esters into the magnetic layer, which have previously been carried out in order to improve the durability of the magnetic recording disk.
Further, with respect to the scratching of the magnetic layer, there are proposed primarily means for mechanically strengthening the layer quality of a magnetic layer, such as the method of improving the binder used for a magnetic layer as disclosed, for example, in JP-A-3-102618, JP-A-3-44818 and JP-A-3-63927; and the method of improving layer quality of a magnetic layer as disclosed in JP-A-3-309913, JP-A-3-150720 and JP-A-3-259466. These methods have been effective to some extent.
Furthermore, in order to increase the function of a liner, there are proposed the method of using a nonwoven fabric made of a mixed yarn of a polyester fiber and an acrylic fiber, or a mixed yarn of a polyester fiber and a rayon fiber as disclosed, for example, in JP-A-1-171176, JP-A-61-208685 and JP-A-1-199371; and the method of impregnating various lubricants into a liner as disclosed in JP-A-61-120386 and JP-A-61-120387.
Also, the method of providing a roughness on the surface of a liner is proposed as disclosed in JP-A-U-62-29678 and JP-A-U-62-22774 (the term "JP-A-U" as used herein refers to a "published unexamined Japanese utility model application").
A reduction in dust released by the liner itself and an excellent cleaning property (dust collecting) are required by the liner for reliability. Further, with respect to running durability, the liner must not scratch the surface of the magnetic layer of a magnetic recording disk and must not cause an increase in torque nor dropout in the high humidity. However, conventional liner materials cannot necessarily provide the best properties.